Rubber-like material and method of producing same



UNITED STATES PATENT OFFICE RUBBER-LIKE MATERIAL AND METHOD OF PRODUCING SAME Theodore F. Bradley, Westfield, N. J., assignor to American Cyanamid Company, New York,

N. Y., a corporation oi Maine No Drawing. Application August 30, 1935,

' Serial No. 38,516

4 Claims. 260-15) This invention relates to rubber-like esters due, the tetra-basic acid anhydride or anhydrides having the property of being heat convertible in resinous form.' without losing their flexibility characteristics, Similarly diand tetra-basic acid anhydrides and to processes of preparing said esters. can be obtained from the reaction of dipentene, 5 The object of this invention is to prepare polyalpha phellandrene, terpinolene, alpha or beta 5 esters or. alkyd complexes of rubber-like rather pinene, or turpentine with malelc anhydride. than of resinous nature, said esters being con- The tetra-basic acid prepared as above was verted by heating intoproducts which are m mixed as follows: fusible and substantially insoluble in most com- 12 n a mon solvents, while yet retaining a high degree 2 r the tetra baslc add hydride 10 of flexibility or distensibility, considerable elas- I ticity and tensile strength. It is a further object a by Weight of tetra ethylene glycolf of this invention to apply and utilize said rubber- This mixture was reacted in the P ce of 08-1- like poly-esters for the production of coatingand boll dioxide and under Daniel reflux ndit 15 impregnating compositions, plastics, molded t e temperature being carried to 200 0. in 15 products and the like. hour and raised o 2 C. in another minutes.

In t m of preparing esters from various The reaction mixture gelled to an infusible form polybasic acids and polyhydric alcohols, it has after 52 minutes at Yielding ery flexigenerally been found and commonly accepted me and re poly-ester.

20 that the glycol esters of the p'olybasic acids are Example 2 r 20 liquid, resinous, or even semi-crystalline products v med b heat to insoluble and Another tetra-basic acid was prepared by refig i igggs y acting the following ingredients as described:

I have found that by condensing certain lcngparts chain glycols having eight or more atom in the Maleic anhydride= mol 49 5 chain se arating-the hydroxy gr ups. w th heat l-a-phellandrene= mol 68 stable acids containing three or more carboxyl The maleic dude was heated o about groups, there are produced a senes of new como my unds havin unique properties and being total- 150 C. and the phellandrene was added slowly PO 5 from a dropping funnel, with frequent agitation 1 different from prior art products in this field. 3

The following, givenpurely by way of illusi g'g 2 g g fi p a-tulle tration arid not in limitation, is one example of 200 iiz s a1; h f fl n 3 Preparing a rubber-like material in accordance 1 m m i all 11 W- th my invention. e 0110- 0 p an ene. Upon W1 allowing the reaction mixture to cool to room Example 1 temperature, it was observed to set to a hard An anhydride of a tetra basic acid having a. crystalline mass- Upon dissolving this mass m molecular weight of about 468 and corresponding 65 Parts of Warm benzene and allowing the solution to stand over night a large yield of white generally to the formula CzsHseOs, was prepared 40'by reacting 75 parts by weight of d-limonene crystalline dim! acid anhydl'lde Obtained.

. 1 This was recovered, washed'with benzene and with parts b3 weight of maleic i i i dried. Several additional crops of the crystalline heating under reflux. In this react1on, which an) i m m d ht M ed a th thermi'c after a temperature of 150 asc ac W n e were 0 R n e becomes n u unde 08s mother liquor was heated to evaporate the volatile 2222x335 fi ggfgizgi fi leastriwo solvents. The residue after evaporation was vacuum distilled and there remained 19 parts of a dieneswhich then combme with male army" non-volatile resinous substance. This resinous g q z zfi fir i a: gg gg ggfig gzz' subistance leg'l1eSl13lltS giboug 1265b? oiitllie gfioduct asicac a an uponan yssisoun o m y can- 50 ents, which are found to be incapable of forming hydride of a tetrwbaslc carboxylic acid having a 50 rubber-like p lyin accordance g the molecular weight of 468 and a neutralization present i ve are removed from e reeeequivalent of 117. This tetra-basic acid is comtion mixture after completion of the reaction by hlned with tetra-ethylene glycol as in Example 1 distillation at a pressure of 10 mm. of mercury and there is obtained a very flexible, rubber-like or less, leaving as a relatively non-distillable resipoly-ester.

The following are additional examples oi'products prepared in accordance with my invention.

Example 3 A condensation reaction is carried out by heating at 150 C., 278 parts by weight of beta eleostearic acid with 98 parts by weight of maleic anhydride. This reaction yielded a partial anhydride of atri-basic carboxylic acid having a molecular weight of 3'76. A flexible product was prepared from this acid by the following method:

7.6 parts by weight of tri-basic acid made from beta eleostearic acid and maleic anhydride 4.5 parts by weight of tri-ethylene glycol This mixture was reacted by heating to 250 C. in 70 minutes and after an additional period of 89 minutes yielded an infusible and very rubberlike gel.

Example 4 v 218 parts by weight of the glycerol tri 'ester of beta eleostearic acid (or beta eleostearine) was condensed with 73 parts by weight of maleic anhydride yielding a viscous liquid of poly acidic nature. 86 parts by weight of tri-ethylene glycol was combined with 222 parts by weight of said material by reacting at 200 to 216 C. until completely gelled or infusible.

Example 5 436 parts by weight of' tung 011 containing from 80% to 85% of alpha eleostearine and the usual impurities (olein) was condensed with 139 parts by weight of fumaric acid yielding a viscous liquid of poly acidic nature. 150 parts by weight of tri-ethylene glycol was combined with 500 parts by weight of said material by reacting at from 200 to 240 C. for several hours until an infusible and rubber-like gel had been obtained.

Example 6 tetra-basic acid anhydride as, for instance, utilizing the method described in Example 2, substituting the dipentene in an equivalent amount for the phellandrene.

This mixture is heated to 250 C. in 2% hours and held. at 250 C.-280 C. for 4 hours until a.

rubber-like gel is obtained.

The foregoing examples represent reactions in which approximately theoretical combining equivalents of the poly glycols and poly-basic acids have been employed and in general such procedure should be used. I do not, however, limit myself to such proportions since it has been found possible to vary the ratios 01' the glycols and polybasic acids to some extent on both the acidic and alcoholic side of the theoretical neutrality point. 7 The use of a theoretical excess of the poly glycols acts to soften the polymers and if carried to excess will inhibit their gelation, while the use of an excess of acidgeneraly reduces the distensibility and increases hardness and will increase the velocity of gel formation unless carried too far in excess.

It is to be understood that the polybasic acids and the anhydrides thereof are strictly equivalents and when the acid-is specified its anhydride is also implied and will be equally as suitable.

Polybasic carboxylic acids containing three or more reactive and heat stable carboxyl groups or ,their anhydride equivalents, and preferably at least four of said groups are generally required for the practice of this invention.

Suitable acids must therefore contain three or more functional carboxyl groups or their anhydride equivalent. Ordinary dibasic acids including phthalic, succinic, adipic, sebacic and certain unsaturated acids which do not tend to associate such as, for example, A-4 tetra hydro .phthalic acid, the dibasic .acid resulting from the condensation of laevo alpha phellandrene with maleic anhydride, the dibasic acids resulting from the condensation of cineole with maleic anhydride and the liquid dibasic acids resulting from the condensation of pinene, limonene, dipentene, terpinolene, commercial terpinene and the like with maleic-anhydride, are all quite unsuitable for the practice of this invention except as they may be employed as modifying or extending agents for special purposes. Even then it is preferred not to use more than 60% of the dibasic acid-glycol products.

While the bulk of the products which are derived by reaction of various terpenes with maleic anhydride are not well suited for the purposes of the-present invention, I have found that these same reactions may result in the formation of some constituents which are suitable for my purpose. Thus, these reactions whichresult in the production of liquid or in some cases of resinous or even of crystalline, dibasicv acid anhydrides in major proportions, also may yield, in addition, minor proportions of tetra-basic acid anhydrides and occasionally of polymers of evenv greater molecular weight and of greater poly basicity. The tetra-basic acid anhydrides and other such constituents of molecular weight in excess of 460 are suitably isolated and recovered in-usable form by distilling oil the dibasic acid anhydrides at pressures of 10 mm. or less and/or by extracting the dibasic acid anhydrides with ligroin or with other light petroleum distillates; leaving the more polybasic constituents as nonvolatile or insoluble residues which may then be utilized for the practice of the present invention.

I am aware that citric acid, a tribasic acid, has previously been combined with glycols and with poly glycols but this acid is highly unstable and when heated to the usual esterification temperatures, rapidly decomposes into di and monobasic acids with loss .of water and of carbon dioxide. Thus, it cannot be classed as a heat stable tribasic carboxylic acid, and on account of-its heatinstability and of the poor water resistance of its derivatives, citric acid is quite unsuited for the purposes'of the present invention, except when employed as a diene reagent in the synthesis of otherfquite different acids. In other words, the acids which I utilize are those which are stable when heated to esteriflcation temperatures.

Various other polybasic acids of the type which react with glycols to yield infusible poly-esters may be substituted in equivalent proportions for lene, ethyl glycols are required, it being especially advantageous to employ poly ethylene glycols such as tri-ethylene glycol, tetra ethylene glycol and the higher homologues of this series. While the particular poly glycol which is to be employed can be varied according to the physical propertim desired and according to the nature of the polybasic acid which is to be used, it is generally I ployed. It is then to be distinctly understood that most polyhydric alcohols other than the poly ethylene glycols of the homologous series beginning with tri-ethylene glycol are not equivalents, except in the sense that they combine chemically in a common manner and that the use of such very considerably alters the physical properties and is usually to be avoided except in special cases where it is deemed advisable to alter the rubber-like nature and increase the hardness or to compensate for the physical characteristics introduced by some particular acid.

it is, however, possible to employ as more acceptable substitutes, long chain glycols other than the poly ethylene glycols, i. e., poly methylene, poly propylene, poly butylene or poly amylene glycols. When desiring to employ such, it is most desirable to select those in which the hydroxyl groups are spaced in the terminal positions of the hydrocarbon chain or in any case as widely apart in the molecule as is possible, since close spacing of said functional groups is not conducive to the development of polymers having' the required degree of elasticity and distensibility. I have found that those alcohols which have at least 10 atoms separating the terminal hydroxyl groups are preferred for my purpose. The distensibility of the rubber-like polyesters is found to be markedly influenced by the chain length of the poly ethylene or other poly glycols used in their preparation, hardness being decreased and distensibility increased as the chain length of the poly glycol is increased. The structure of the acids likewise affects the physical properties of the polymer but in general exert less influence than does the structure of the poly glycols and in any case the effect of the acid may be suitably compensated by appropriate selection of the glycol. In general, it is found thatboth in the case of the acids and of the glycols that the further apart the reactive groups (1. e., carboxyls or hydroxyls) are spaced in the molecule, the more distenslble are the resulting poly-esters.

The rubber-like polymers of this invention can be prepared and fabricated for industrial use in a number of ways. Thus, one may interrupt the initial esteriflcation reaction prior to the gelation and while the condensation polymers are still in the A stage, when organic solvents of the type of acetone, cellosolve, .benzene; toluene, xylactateand the like my be added singly or in admixture. Buchpolutions can be employed as coating or impregnating compositions'either with or without the addition of pig ments and/ or other additions or extenders. Fillers can be admixed with the solutions, the sol.- ve'nts evaporated and the mixtures then subjected to elevated temperatures ranging usually from 150 to 250 C., to convert the-polymers to infusible and insoluble form.

The new poly-esters may also jacketed rubber or dough mixers at a suitable be prepared in elevated temperature and either in the presence -or absence of pigments, fillers or other-extending agents. While the chemical reactions are efiected and carried to the s'o-called A, B or C stages as desired, the reaction mixture is subjected to constant agitation or mastication. This method of production is particularly desirable in order to expedite the condensation and to complete the cure and is especially advantageous during the conversion of 3 stage polymers to C stage material. The use of partial vacuum and/or of inert gases such as carbon dioxide or nitrogen is usually of substantial benefit when manufacturing the polymers by the aforesaid process.

Those polymers or compositions containing the same which have not been fully cured to the C stage, but which closely approach the same, have been found to be capable of being molded to desired shape in hydraulic presses by the usual methods well known in that art. The molding operations in this case are merely for the purposes of compacting the material and of fabrication to shape and unlike the phenol or urea and formaldehyde plastics is not employed to effect a cure since curing of my materials can best be properly efiected under conditions which permit of the free escape of volatile matter. Following the molding operation, the compositions may be subjected to additional heat treatment to complete the cure.

The curing of these plastics is a vitally important matter since the physical properties, notably strength, distensibility, elasticity, water resistance, oil resistance, etc., are very profoundly influenced by the same. Curing is usually best effected in an inert atmosphere since, especially in the case of those polymers which contain unsaturated linkages, oxidation Will occur with attendant loss of distensibility and elasticity. Curing in the presence of air is generally employed whenever increamcl hardness is desired or the time factor is of vital importance.

Temperatures in excess of C. and generally within the range of to 250 C. are ordinarily required to effect a cure, the exact time of cure ranging from an hour to several weeks according to the thickness of'the specimen, the nature and amount of fillers admixed or of the surface which has been coated or impregnated, of the temperatures employed and of the extent to which the 7 environmental conditions allow and facilitate the escape of volatile constituents during the process. It is impossible to specify an exact cure unless all other conditions be known, but in general the cure is best carried on until the progressive loss in weight during said treatment ceases or reaches a very small value and when test specimens exhibit the minimum water absorption upon immersion test.

Some of the thoroughly gelled and infusible substantially B stage polymers of the aforesaid examples were removed from the reaction kettles and placed on mixing rolls where they were incorporated with 50% by weight of medium iibered asbestos and the resulting mixtih'es then worked Tensile strength kgs. per sq. cm.

Composition of example number asses Montague:

The control consisted of the product obtained by reacting 2 mols of glycerol with 3 mols of sebacic acid and carrying out the reaction to the infusible or gel state. This gel was admixed with asbestos, sheeted and cured in the same manner as the other products listed. It is evident that the control is appreciably weaker and much less distensible than are the products of this invention. The combination of glycerol and sebacic acid were chosen since this material is noteworthy in the field of alkyd resins for its flexibility and rubber-like qualities.

Composition #1 represents a preferred type of the new rubber-like polymers, namely that produced from a tetrabasic acid and tetra ethylene glycol. The inclusion of dibasic acid as in #6 exerted a plasticizing action and permitted the use of tri-ethylene' glycol. However, when ethylene glycol or even di-ethylene glycol was substituted for the tri-ethylene glycol of #6, the rubber-like qualities were seriously impaired.

In the case of a tri basic acid polymer such as is represented by #3, fairly satisfactory strength and distensibility were secured from the tri-ethylene glycol ester although both values were appreciably lower than with the tetra basic acidtetra ethylene glycol polymer. In this, as in the preceding cases, the substitution of lower molecular weight glycols resulted in substantial loss of distensibility.

The maintenance of high strength, yet coupled with a notable improvement of distensibility as compared to the compositions of the priorart is characteristic of the present invention.

The compositions of this invention may frequently be suitably modified with non-drying or drying oils or with derivatives of the same including mono or di glycerides, free fatty acids, polymerized oils, partially oxidized or blown oils, vulcanized oils and the like. They may also be modified by admixture and/or reaction with phenolic aldehyde resins or condensates, vinyl esters or polymers, urea-aldehyde condensates, rosin, ester gum, and the fossil resins or their esters. Such. modification is occasionally advantageous,

especially in the field of coating compositions. Furthermore the use of. monohydric alcohols and of esters, which latter may include alkyl'phthalates, alkyl or aryl phosphates, etc. as plasticizers is not precluded. Further it has been found that the compositions of this invention may be admixed and compounded with natural or synthetic rubber and with Duprene and sheeted or extruded to desired form.-

Brake blocks of the molded type and laminated or impregnated brake linings, clutch facings and friction members have been made from some of the compositions of this invention and in a number of cases have been found to excel similar advantageous.

Other suitable changes maybe made in carrying out the invention without departing from the spirit and scope thereof except as defined in the appended claims.

.I claim:

1. The process of preparing. infusible, flexible, rubber-like resins which comprises reacting a long-chain glycol having at least eight atoms in the chain separating the esterifiable hydroxyl groups with a heat-stable polybasic acid material containing at least 40% of an esterifiable tetrabasic carboxylic acid, said acid material being derived from the chemical combination of an alpha-beta unsaturated polycarboxylic acid and a substance taken from the group consisting of terpenes and diene compounds, and continuing the reaction by heating between ISO-280 C. for sufficient time to produce. an infusible and substantially insoluble, rubber-like condensation product. A

2. The process of preparing infusible, flexible, rubber-like resins which comprises reacting a polyethylene glycol of the homologous series beproduct.

. 3. The process of claim 1 in which the initial reaction product is mixed with a filler priontocontinuing the reaction by heating.

4. An infusible, insoluble and flexible rubber- I like material produced by the process of claim 1.

THEODORE F. BRADLEY. 

